This invention relates to a method and apparatus for creating a surface on an eyeglass lens blank satisfying given prescription data, which lens blank thereafter being cut about its edges to conform it to a shape to be fitted into a frame in a pair of prescription eyeglasses, and deals more particularly with an improvement in such a method and apparatus wherein from the data normally provided in a prescription, machine operating data are compiled causing a prescribed surface to be cut in the lens and thereafter causing the lens blank to be edged while mounted on the same block used during the surface cutting operation.
A common procedure in making a lens for a pair of prescription eyeglasses is to provide a lens blank, of glass or plastic having two major lens surfaces one of which being a finished surface and the other being one which is worked to satisfy a given prescription for a wearer. Hitherto, prior to surface cutting of the blank to conform it to the given prescription, any cylinder axis called for by the prescription had to be oriented coincidentally with the general horizontal axis of the block. This labor and skill intensive step was to insure that the lens cylinder axis was aligned with the horizontal axis of the lap when the blocked lens and lap were placed in a lapping or fining machine. Maintaining this relationship between the lap tool and the surfaced lens was important in order to effect proper alignment and full working of the total cylindrical surface during the fining or lapping operation. The edge shape of the lens is copied from a pattern mounted on its geometric or box center and on the horizontal axis of the eyeglass frame. Thus, it is necessary to release the original block from the lens and thereafter reblock it with a second block so as to orient the block center and its axis of rotation coincidentally with the box center and horizontal axis of the eyeglass frame. This reblocking process has been known to be very labor and skill intensive in that it requires the skill of technicians to exactly locate and mark critical points on the lens with an inking device and the subsequently attach the new block to the blank using these marked points such that the blank axis of rotation is coincident with the geometric or box center of the lens pattern. Thereafter, the lens blank and the second subsequently attached block are rotated about a common axis of rotation in a edging or cutting machine, which axis also serving as the center point of the pattern or from which the "spokes" defining the amount of radial cut in the blank are referenced.
While some attempts have been made to computerize data preparation, such as disclosed in U.S. Pat. No. 4,656,590 issued in the name of Ronald Ace on Apr. 7, 1987, such systems have nevertheless been unable to continuously maintain a lens blank on a single mounting block throughout the entire operation beginning with the surface cutting operation through to the final edging step. Although in other systems, such as disclosed in U.S. Pat. No. 2,352,616 issued in the name of Canning on Jul. 4, 1944, it is known that a lens block may have a disposable portion and may support the lens both during surfacing and edging, it is nevertheless necessary to mechanically shift the support block on the drive of the surfacing machine, the fining machine and/or edging machine to align the block axis of rotation with the desired one of the optical or geometric centers to correctly align the cylinder and horizontal axes. Such mechanical shifting operations introduce additional time into the lens making process and further are the source of possible errors and increased labor costs by requiring a higher degree of skill to be practiced by the technician operating the machine. In addition, the Canning patent requires the use of a permanent holder portion of the lens block. This permanent holder adds a further assembly step to the blocking procedure and introduces a chance for error and misalignment. Further, the permanent holder must be small in diameter to permit edging the lens to fit a very small eyeglass frame without cutting the holder. This prevents the holder from providing solid support for the disposable portion of the lens block and the lens itself during the surfacing operation. Such support is critical to enable accurate generation of the optical surface.
Conventional lens blank and block mounting assemblies have in the past presented other problems and disadvantages with their use. In particular, the surfacing blocks assembled with the lens blank hitherto have for the most part been made of metal. The adhesive used for adhering the lens blank to the metallic block was a low melt metallic adhesive which when applied to the front surface of the lens blank, caused it to be bonded to the metal block as long as the adhesive was not exposed to its melting point, usually equal to about 117 degrees F. One drawback associated with this type of assembly is in the type of metal based adhesive used to secure the metallic block to the blank. Here metals, such as bismuth, cadmium or the like, which have been proven to be hazardous to the health of those working with it are used. In addition, in systems wherein the blank is subsequently remounted to a second, usually metal block used for edging usually after the lapping process, the second block is substantially smaller offering less supporting surface area than the surface area of lens to be supported in order to allow the edging tool to cut the designated path about the lens without interfering with the second block supporting it. Moreover, because the lens blank has now undergone surface cutting and polishing thus making it more susceptible to cracking, the less than adequate support offered by the second block increased the possibility of lens cracking or slipping on the block during the edging operation. Also, in these previously known systems in which double blocking is necessary, each metal block associated with the surface treatment process whether for the purpose of surface cutting or for edging a pattern in the lens could not be mounted to a lens until first being aligned with a required axis to be found from the data supplied by the prescription and the eyeglass frame shape. As such, these metal block and lens blank assemblies could not be put together as preforms and subsequently shipped for storage and inventoried for use at a later point in time when needed. Rather, they were required to be assembled on site according to requirements of the involved prescription to be satisfied. As a result, these known systems experienced drawbacks in the marketplace as well as increasing the time and labor expended by the technician in setting up the block prior to forming the desired surface contour on the involved lens blank.
Accordingly, it is an object of the present invention to provide a method and a related system for both surface treatment and edging of an involved lens blank face using a single disposable and inexpensive block which is one-time mounted to the lens blank before beginning the surface cutting process and is subsequently used throughout the remaining steps of the operation for holding the lens blank in other machines for the purpose of finishing and edging the lens blank thereby avoiding the aforementioned problems associated with previously known systems in which reblocking of the lens blank is necessary.
In keeping with the foregoing object, a more specific object of the invention is to provide a lens making system of the aforementioned type to be used with a lens blank and block assembly wherein means are provided in the system for receiving as input data related to lens surface characteristics and data defining the shape of the frame to be edged, which data in turn being used to create numeric machine operating language for instructing automated tools for cutting a prescribed surface contour in the lens blank and thereafter for edging the blank to conform it to a particular shape to be fitted within an opening in a selected frame while using the original lens blank and block assembly.
Still a further object of the present invention is to provide a system and a method whereby using a single blocking step, and a given frame shape taken in conjunction with an ophthalmic prescription surface, lenses for an eyeglass pair are quickly fabricated without requiring excessively skilled operators.
Still a further object of the present invention is to provide a novel block for use in a lens blank and block assembly having means for mounting it to a variety of different tools for working a lens blank during surfacing, polishing and edging operations.
It is still a further object of the present invention to provide a block capable of totally supporting the prefinished surface of a lens blank mounted to it while nevertheless being capable of allowing excess lens material to be cut away with it during an edging operation in order to create the selected shape for fitting into a frame.
A further aspect of the invention lies in a lens blank and block assembly wherein the lens blank is attached to the block through the intermediary of an adhesive bonding means which adhesive bonding means being generally non-toxic to its user and being capable of being stored for prolonged periods, such as in inventory.
Still a further object of the present invention is to provide a numerically controlled machine of the type having a memory in which data stored as numeric machine operating code defines a number of different frame patterns, a selected one of which patterns being chosen and used to control the movements of an edging tool to cut a designated frame pattern into the lens blank and block assembly.
A further object of the present invention is to provide a quick release mounting means for a lens blank and block assembly used in a lens surface cutting apparatus such that the lens blank and block assembly is readily mountable to a rotating chuck in a single orientation thereby further reducing the time and mistakes otherwise associated with mounting of the lens to a surface cutting machine.
Other aspects and objects of the invention will become apparent from the following disclosure and appended claims.